Tachometer and revolution counter for internal-combustion engines



Nov. 4, 1952 M. PETROFF 2,617,083

TACHOMETER AND REVOLUTION COUNTER FOR INTERNAL-COMBUSTION ENGINES Filed Nov. 1, 1947 flaws.

Patented Nov. 4, 1952 TACHOMETEEAND REVOLUTION COUNTER FOR INTERNAL-COMBUSTION ENGINES Merlin Petroff; Lake Geneva, Wis., as'signor to Stewart-Warner Corporation, Chicago, 111., a. corporation of Virginia Application November 1, 1947, Serial No. 783,491

3 Claims.

My invention relates generally to tachometers and revolution counters particularly adapted for use in indicating the speed and registering the total number of revolutions of an internal combustion engine having spark ignition.

In internal combustion engines as used in automobiles, airplanes, and the like, employing spark ignition, the revolutions per minute and the aggregate revolutions of the engine may, in accordance with the principles of the present invention, be readily determined by apparatus responsive to the operation of the ignition system.

It is thus the primary object of the invention to provide an improved speedometer or tachometer and revolution counter for use with an internal combustion engine having a spark ignition system, in which the only connection to the engine is an electrical connection to the ignition system.

A further object is to provide an improved revolution counter and speedometer for internal combustion engines having spark ignition systerns, which is simple in construction, may be economically manufactured, and which is reliable in operation.

Other objects will appear from the following description, reference being had to the accompanying drawings, in which:

Fig. 1 is a circuit diagram of the electrical parts of the apparatus; and

Fig. 2 is a fragmentary perspective view of the mechanical parts of the apparatus.

Referring to Fig. 1, there is shown a more or less conventional normally closed circuit ignition system comprising a transformer ll having a primary winding I and a secondary winding l2. The primary winding I0 is connected between the ungrounded terminal of a battery I4 and a conductor I6, While the secondary winding i2 is connected between the conductor 16 and the rotating contact arm I8 of a conventional distributor. The arm I8 is adaptedto make electrical connection with contacts 20, respectively connected to spark plugs 22 forming part of the internal combustion engine. In the circuitv oi Fig. 1, it is assumed that the engine is of the six cylinder type, and there are therefore six equally spaced contacts 20 connected respectively to the six spark plugs.

The circuit through the primary winding I0 is normally completed to ground through a circuit breaker switch 24, the movable arm 26 of which is connected to ground and thus to the grounded terminal of the battery M. The resiliently biased arm 26 is operated by a breaker cam 28 having six high points, the cam being-connected to the distributor switch arm It so as torotate therewith. the arrangement being such that the contacts 24 of the breaker are separated at the instant that the switch arm I8 is in engagement with one of the contacts 28. When the breaker contacts 24 are separated, a condenser 30 connected across the contacts of the breaker contacts 24 charges and causes the spark at the connected spark plug 22 in the customary manner.

As thus far described, the circuit is conventional for internal combustion engines as used on automobiles and the like. It will be clear that the circuit breaker operates at a speed proportionate to that of the engine, and thus the electrical pulses produced as the condenser 3811s rapidly charged, may be used to provide a basis for measuring the speed of the engine. and counting the number of revolutions thereof In accordance with the present invention, this is accomplished by connecting a high resistance coil 32 in parallel with the condenser 38 the resistance of this coil being so high relative to the capacity of the condenser 30 that the connection of this coil in the. ignition. circuit doesnot interfere with the operation of the latter. The coil 32 forms part of a relay having a singlepole :double throw switch arm 34 which is normally biased to make contact with an upper contact 35, and, when thecoil 32 is energized, makes contact with a lower contact 38.

The relay switch arm 3t and. the contacts thereon are of very small mass so as to be capable of vibration at the speedat which the circuit breaker contacts 24 open and close, and is connected to the ungrounded terminal of. battery M. The contacts 36 and 38 are respectively connected to the opposite ends of a primary winding- 48' of a transformer 42, the center tap M of which is connected to ground. Thus, as the relay switch arm 34 alternately engages contacts 36 and 138, an alternating flux will be set up in the trans former 42.

The secondary winding 45 v of the transformer 42 has its center tap 48 connected to ground. and has one terminal connected to ground through a phase changing resistor 59 and a field winding 52 of a synchronous motor 54, and has its other terminal connected to ground through a second field winding 56 of the synchronous motor 54-. A buifer condenser 58 is connected across the terminals of the secondary winding 45 so as to decrease the eifect of transients.

Thus, as the relay switch arm 34* alternately contacts the contacts 35 and 38, alternating currents of different phase will flow through the field windings 52 and 56 of the synchronous motor 54.

As shown in Fig. 2, the synchronous motor 54 comprises field laminations 60, a laminated rotor 62 having a rotor shaft 64 mounted in suitable bearings. The shaft 64 has one or more permanent magnets 56 secured thereto to provide a magnetic field for the operation of a drag cup 68 made of a nonmagnetic conductor, such as aluminum, the cup being carried by an arbor Ill mounted in a suitable bearing and being normally biased to move counterclockwise by a hair spring 12, one end of which is connected to the arbor 10, the other end being secured to a bracket 14 mounted on the motor frame. The arbor carries an indicating hand 16 cooperating with a dial (8 suitably graduated in R. P. M. or in motor miles per hour.

The rotor shaft 64 also carries a worm ear 80 meshing with a worm wheel 82, which,

. through a speed reducing gearing including shaft .84, pinion 86, idler gear 88, gear 90, pinion 92,

and gear 94, drives an odometer shaft 96 for the operation of a revolution counter 98 which may be of conventional construction.

From the foregoing, it will appear that each time the circuit breaker contacts 24 open and close, electrical current will flow alternately in the two halves of the primary winding 40 of transformer 42, and that the alternating current thus induced in the secondary winding 46 will be supplied to the synchronous motor 54 to cause operation thereof at a speed proportionate to that of the internal combustion engine.

If the engine has a number of cylinders other than siX, the number of poles of the synchronous motor may be changed accordingly, or as an alternative the tension applied by the hair spring 12 on the drag cup 68 may be changed, while at the same time changing the ratio of the speed reduction between the worm 8E! and the counter drive shaft 96.

It will be clear from the foregoing that to utilize the apparatus of the invention, it is necessary merely to connect the high resistance relay coil 32 across the circuit breaker contacts 24 and to connect the switch arm 34 of the relay to the ungrounded terminal of the battery 14, and that no other mechanical or electrical connections to the internal combustion engine are required, When the apparatus of the invention is used on an automobile, the dial 18 may be calibrated in miles per hour and the counter 98 have a gear reduction such as to indicate motor miles. The motor miles will, of course, not be exactly equal to the miles traveled by the vehicle, but will be indicative of the mileage which would have been traveled by the automobile had it been driven in high gear continuously. In so far as an indication of the use of the motor is important, the indication of the counter 98 will be more accurate than a conventional odometer connected to the drive shaft or wheels of an automobile. Thus, for example, the counter of the present apparatus will serve as a more reliable indication of the efficiency of the motor on the basis of miles per gallon of fuel than a conventional odometer. However, in normal uses of an automotive vehicle, the motor miles indications of the counter will be sufficiently accurate with respect to actual miles traveled as to make any slight error of little consequence.

When used on an automobile, the indication of the pointer it is of interest nearly exclusively when the automobile is in high gear. so that the 4 pointer 16, which actually indicates motor miles per hour, may, for all practical purposes, be considered as indicating the speed of the automobile in miles per hour. When used on an airplane the instrument serves as a tachometer and engine revolution counter.

While I have shown and described a preferred embodiment of my invention, it will be apparent that numerous variations and modifications thereof may be made without departing from the underlying principles of the invention. I therefore desire, by the following claims, to include within the scope of the invention all such variations and modifications by which substantially the results of my invention may be obtained through the use of substantially the same or equivalent means.

I claim:

1. In an apparatus for indicating the revolutions per minute of an internal combustion engine provided with a source of direct current and an ignition system having a circuit breaker operating in synchronism with the engine, the combination of a high resistance relay winding connected across the circuit breaker contacts of the ignition system, a relay switch operated by flux generated in said relay winding, said relay switch having a switch arm connected to one pole of a direct current source of electrical energy, a pair of contacts alternately engaged by the relay switch arm, a transformer having a center tapped primary winding with the terminals thereof connected to said contacts, means connecting the center tap of said primary winding to the other terminal of said source, and a synchronous motor having a pair of windings respectively connected between the opposite ends of the secondary winding of the transformer and a center tap thereon.

2. In an apparatus for indicating the number of revolutions of an internal combustion engine provided with an ignition system having a circuit breaker operating in synchronism with the engine and having a source of direct current, the combination of a high resistance relay winding connected across the circuit breaker contacts of the ignition system, a relay operated by flux generated in said relay winding, said relay having a switch arm connected to one pole of the direct current source of electrical energy, a pair of contacts alternately engaged by the relay switch arm, a transformer having a center tapped primary winding with the terminals thereof connected to said contacts, means connecting the center tap of said primary winding to the other terminal of said source, and a synchronous motor having a pair of windings respectively connected between the opposite ends of the secondary winding of the transformer and a center tap thereon.

3. In an apparatus for indicating the speed of an internal combustion engine provided with a source of direct current and an ignition system having a circuit breaker operating in synchronism with the engine, the combination of a relay having a high impedance winding connected in parallel with a, circuit breaker and thereby made responsive to the interruption of the ignition circuit by the circuit breaker, a transformer having a primary winding with a center tap connected to one terminal of the source, a single pole double throw switch having its movable part connected to the other terminal of said direct current source, means connecting the fixed poles of said relay switch respectively to the ends of the primary winding, the secondary winding of said transformer having a center tap connected to one terminal of the source, and a synchronous motor connected between the other terminal of said source and the terminals of the secondary windmg.

MERLIN PETROFF.

REFERENCES CITED The following references are of record in the file of this patent:

Number Number 6 UNITED STATES PATENTS Name Date Bird Nov. 10, 1936 Breer Aug. 24, 1937 Jones Feb. 8, 1938 Le Fevre May 23, 1939 Hegelby Aug. 20, 1940 Norman Jan. 18, 1944 FOREIGN PATENTS Country Date Great Britain Oct. 23, 1930 

